Automatic resistance-controller.



L. BRADLEY.

AUTOMATIC RESISTANCE CONTROLLER.

APPLICATION FILED IAN-22, I914.

Patented July 18, 1916.

Ill

UNITED STATES. PATENT oFFIoE.

LYNDE BRADLEY, OF MILWAUKEE, WISCONSIN.

. AUTOMATIC RESISTANCE-CONTROLLER.

Specification of Letters Patent Patented J [11y 18, 1916.

Application filed January 22, 1914. Serial No. 813,665.

; My invention relates to lmprovements in automatic resistancecontrollers of that type in which a compressible resistance medium isemployed, such for example as the column of carbon disks shown anddescribed in a. former patent, numbered 1054902, dated March 4, 1913,issued to L. and H. L. Brad ley, for resistance devices.

.The ject of my invention is to provlde means for automatically varyingthe pressure upon acompressible resistance member in proportion tovariations in conductlvlty dueto temperature changes, whereby theresistance or3conductivity of the medium may be kept substantiallyconstant. I am thus enabled to adjust the pressure upon my improvedresistance column at the initial or starting temperature and no furtherchanges in manual adjustment will be required to maintain a constantresistance notwithstanding the rise in temperature due to the passage ofthe electric current through the resistance medium.'

In the dr'awingsFigure 1 is a front elevation of a current controllerembodying my invention, in which a pair of resistance columns isemployed. Fig. 2 is a side elevation with one of the columns removed, online mw of Fig. 1, portions of the frame and clamping members beingshown in cross section.

Like parts are identified by the same reference characters in bothviews.

The resistance columns are similar to those shown in my former. patentabove referred to. Each column comprises a series of carbon disks 1mounted in a tubular casing 2 against insulating head pieces 3. Thecolumn inclosing casings 2 are supported from a backing or plate 5 by aspider frame 6 and connecting bolts 7, said frame 6 being provided withclamping members 8 and 9, which are adapted to embrace the tubularcasings 2, to which they are secured by clamping bolts 10. The clampingmembers 8 and 9 are insulated from the casings 2 by sleeves 11 ofasbestos or other suitable material. Pressure is applied to the columndisks 1 by means of rods 12, which extend through the end caps 13 of thecasings and bearupon end disks 14: which cap the ends of the columns.The rods 12 are actuated by means of a pressure applying bolt 15threaded in a traveling nut 16, the motion of which, when actuated bythe bolt, is transmitted to the rods 12 through a set of pivot pins 17and a frame 18 having outwardly pro ect1ng arms 19 bearing against thein sulated heads 20 on the outer extremities of said rods 12. The bolt15 is provided with a head22 and operating handles 23, the head beingadapted to bear upon the backing 5 or upon a bearing plate 24.interposed between it and said backing. The other endv portion of thebolt passes loosely through a central aperture 25 in the spider member 6and is provided with an end nut 26. A spiral spring 27 is interposedbetween the nut Y26 and the spider member 6.

When the bolt 15 is turned in a direction to apply pressure to the heads20 of the rods 12, such pressure is transmitted through the carbon disksto the outer or free ends of the casings 2. The casings 2 therefore pulloutwardly upon the spider member 6, which is clamped to the casings bythe members 8 and 9. This outward pull upon the spider member draws itforcibly against the spiral spring 27, compressing the latter. Thecolumns are thus placed under the resilient reactionary pressure of thespring 27, that is to say, each of the columns is pushed by its rod 12against a resilient cushion.

The casings 2 are formed of a material which expands under the influenceof-heat, thereby tending to relieve the pressure upon the disks 1, asthe heat generated by the current passing through the columns, increasesthe temperature of said casings. It has been found by experiment,however, that it is virtually impossible to secure aocurate regulationof these variations in pressure by selection of an appropriate materialor composition .for the casings 2, since the carbon disks arecomparatively inelastic utilize the reactionary and expansive pressureof the spring to ofi'set to some extent the expansion of the casing,whereby a very slight variation of pressure upon the carbon column issecured. It will of course be understood that the nut 26 is locked uponthe bolt 15 by any suitable means, such as the pin 30, said nut havingbeen previously adjusted in its proper position upon said bolt.

In operation, the columns being without pressure, it is merely necessaryto actuate the handles 23 to rotate bolt 15 in a direc-- t1on to causenut 16 to move outwardly 011 said bolt, said nut being prevented fromturning with the bolt by forked arms 31, which loosely engage thesupporting bolts 7. The motion of the nut will then be transmitted, asabove explained, through the arms 1.9, head 20, and compression rods 12to the disks 1, thus compressing said disks against the outer or freeends of the tubes 2, said pressure being transmitted through the tubesand the spider 6 to the resilient cushion formed by the spring 27. Thepivot pins 17 and frame 18 permit an equalization of pressure upon thecompressing rods 12 of the respective columns. The screw 15 will beturned until the desired pressure upon the columns is secured, whereuponthe resistance of the columns will be reduced in accordance with thepressure exerted, until-the required conductivity is attained, asdescribed in my said former patent. If no changes in conductivity arerequired, the device may then be left without any further manualadjustment. An electrical current passing through the column or 001-umns will have no substantial effect upon the conductivity thereof onaccount of the temperature rise necessarily developed therein, for thereason above stated, that the casing tubes will expand and cause aslight diminution in pressure suflicient to compensate for the increasedconductivity which would result from the increase in pressure due toheat if the casing tubes 2 were not lineally expansible.

The specific construction illustrated, by which the spring is locatedoutside of and away from the columns is intended to remove the springfrom the influence of heat developed in the columns from the currentwhich traverses them. The apparatus is of course adapted to offset theeffects of temperature variations due to either internal or externalcauses, but external temperature variations will not ordinarily be suchas to affect the durability or resiliency of the spring. I thereforeprefer to separate the spring cushion from the column or columns insteadof inserting it between the disks and the end of the column. or betweenthe disks and the compression rods 12. But aside from the effects ofheat upon the resilient cushion, its specific location in the line alongwhich the material.

I claim 1.. An automatic resistance controller for compressiblerheostats, comprising the combination with a set of compressibleresistance columns, and compressing means, of an abutment, a resilientcushion located between the columns and interposed between the abutmentand the compressing 7r means, and a thermostatically operated memberadapted by expansion, to relieve the pressure upon said cushion.

2. The combination with a current controlling compressible resistancemcmber, of a thermostatically expansible' casing therefor, means forcompressing said member within the casing, and avresilientlycushionedabutment supporting said casing and to which the pressure is transmittedthrough said casing.

8. In an electric current controller, the combination of a plurality ofcompressible resistance mediums, containers for said mediums, means forproducing pressure on said mediums, means for equalizing the pressure onsaid mediums, and supporting means for said containers, said containers,at the ends opposite to those upon which the thrust of the resistancemedium is received, being attached to but insulated from, saidsupporting means near the end at which the pressure is applied.

4. In anelectric current controller, the

pressure is exerted, is notyery combination of a compressible resistance10o medium, a container for said medium, means for producing pressure onsaid medium, and a support attached to, 'but' insulated from saidcontainer at the end opposite to that upon which the thrust of theoompressed resistance medium is received and near the point where thepressure is applied.

5. The combination with a compressible resistance medium for controllingelectric circuits, 2. spring adapted to maintain said medium underpressure, a member expansive under the influence of heat, means forheatingsaid member, means for utilizing the expansion of said membertovary the tension of said spring in such proportion to its variation inconductivity due to heat, as to maintain a substantially constantconductivity of said resistance medium.

6. In an electric current controller, the combination of a compressibleresistance medium and container for said medium, said containerexpansive under the influence of heat and exposed to the heat of saidmedium, means for compressing said medium, a support for said containerattached to and insulated from said container at the end opposite tothat upon which the thrust of the compressible resistance medium isreceived, a spring for maintaining pressure me ers on said medium andmeans for utilizing expansion of said container to vary the tension ofsaid spring in such proportion to the variation in conductivity of theresistance medium as to maintain a substantially constant resistance.

7. The combination of a set of compressible resistance columns, a casinginclosing each column, clamping members embracing said columns, a rodextending through one of the clamping members, a cushion springinterposed between one end of the rod and said clamping member, a nutscrew threaded onsaid rod, a pressure bar pivotally connected With saidnut, and insulated posts interposed between the columns.

8. The combination of a set of compressible resistance columns, athermostatically expansible casing for each column, a support for saidcasings, a screw having resilient swivel connection with the support,and a nut on said screw in pressure relation to the columns.

In testimony whereof I aflix my signature in the presence of twowitnesses.

LYNDE BRADLEY.

pressure bar and said \Vitnesses LEVERETT C. WHEELER, IRMA D. BREMER.

